im not sure this is a more of a matter of linguistics or psychology.

one friend of mine refers to obama as "the nigger", not once, not twice, but constantly during a conversation. i'm sure he does this around other people, so evidently there is at least one social circle where this use of language is acceptable.

the way santorum started off lead the listener to anticipate "the N word", and it seems that santorum's mouth got just a little bit ahead of his brain, and when his brain heard what his mouth was about to say, he stumbled, stammered, and hunted for a way to recover. this Freudian slip boggled his mind pretty good, and scattered his thoughts for a long moment. he was already considering the consequences of what he was about to say. he decided against dropping the N bomb, but it gives you an idea of how his brain works and what he thinks about obama and black people in general.